1. Field of the Invention
The present invention relates to a method for reducing the rate of registration in code division multiple access (CDMA)-based mobile networks. The method prevents a traveling mobile device, such as a cellular telephone enabled for CDMA, for example, from registering within a new, or secondary, registration area, prior to physically relocating from a first, or current, registration area to the new registration area.
2. Description of the Related Art
Code division multiple access (CDMA) is a multiplexing scheme which encodes data with a special code associated with each channel utilized by a mobile device, and uses the constructive interference properties of the special codes to perform multiplexing operations. One of the advantages of the CDMA methodology is that a “soft handoff” may be performed by a mobile device. A soft handoff, as the technique is commonly referred to in the art, includes the addition of a second base station transceiver subsystem (BTS) to a connection to improve the link budget for users on the edge of a cell. As a result, signal quality and handoff robustness are both improved for edge users in a CDMA system.
In the CDMA system, neighboring cells typically all use the same frequency for transmission and the cells, or base station subsystems associated with each cell, are distinguished by means of a number, commonly referred to as the pseudo-noise (PN) offset. The PN offset is a time offset from the beginning of a well-known pseudo-random noise sequence, which is used to spread the signal from the BTS. With all of the cells operating on the same frequency, digital signal processing based on the offsets from the PN sequence is required to listen to different base station subsystems, rather than radio frequency (RF) transmission and reception based on separate frequencies.
As a CDMA enabled mobile device, such as a cellular telephone, for example, roams through its associated cellular network, the mobile device detects the PN offsets of the neighboring cells and reports the strength of each signal back to the reference cell of the call (usually the strongest cell, in terms of signal strength). If the signal from a neighboring cell is strong enough, the mobile will be directed to “add a leg”, as the process is commonly referred to in the art, to its call, and start transmitting and receiving to and from the new cell, in addition to the cell (or cells) already hosting the call. The signals generated by each BTS associated with a particular cell, used for registration, are commonly referred to as “pilot signals” in the art, as they are used for guidance of the mobile device communications.
Likewise, if a cell's signal becomes too weak, the mobile device is directed to “drop” that particular leg. Following this procedure, the mobile device can move from cell to cell and add and drop legs as necessary, in order to keep the call up without ever dropping the link, and interrupting communications.
With the rapid deployment of mobile services around the globe, service providers are presently either using or planning to use a pure CDMA technology, or a technology that is based on CDMA, such as the Universal Mobile Telecommunications System (UMTS), for example. One key process by which the mobile device identifies its location and parameters to a BTS is through “registration”. Through registration, the CDMA-based mobile network is able to route incoming calls properly to the desired mobile device.
The present standard of the Telecommunications Industry Association (TIA), commonly referred to as the TIA-2000.5-D standard, provides twelve different types of registration methods implemented in CDMA networks, namely: (1) power-up; (2) power-down; (3) timer-based; (4) distance-based; (5) zone-based; (6) parameter-change; (7) ordered; (8) implicit; (9) traffic channel; (10) user zone; (11) encryption/message integrity re-sync required; and (12) broadcast multicast (BCMC). The first six forms of registration listed above are commonly referred to as “autonomous registration”. In autonomous registration, the mobile device initiates a registration process based upon a particular criteria, for example, turning on or off the mobile device, expiration of a timer, entering a new area or zone, or the distance between the new cell associated with a particular BTS and the last visited cell associated with the previous BTS exceeding a particular threshold.
All types of CDMA registrations, particularly the mobile device-initiated autonomous registrations, have a direct impact and effect on the CDMA access channel and the paging channel capacities, as well as the capacities of the network entities, such as, for example, the BTS, the base station controller (BSC), the mobile switching center (MSC), the home location register (HLR), and the interconnecting links. It would be desirable to reduce the rate of CDMA registrations which a mobile device makes, as this reduction will help to maximize the usage of the system capacities, including the access channel capacity, the paging channel capacity, and the network entities' capacities.
The rate of the mobile device registration is dependent upon a wide variety of factors, such as, for example, the proximity of the mobile device to a registration boundary. In this exemplary case, the parameter-change registration may yield a high amount of mobile device registrations due to the fact that random RF environment changes on the registration boundary (due to, for example, the mobility of mobile device users and other sources of scattering) may bring about a change in the mobile device's parameters which requires the mobile device to perform a parameter-change registration.
In order to minimize such a possible high rate of registration, either a registration method based on the expiration of a timer (i.e., timer-based or zone-based registrations) or a distance-based registration may be utilized. However, using a method of registration based upon the expiration of a timer may lead to the problem of missed calls, particularly in cases where the mobile device crosses the registration boundary between two MSCs. As an example, we may consider a scenario where a mobile device has passed between two registration areas, but the timer did not expire. Thus, the mobile device did not update its location through registration while a call to the mobile device was incoming. If the MSC does not cover the area that the mobile device is currently visiting, the call will be missed by the mobile device, even if the timer has not yet expired.
A distance-based registration methodology also does not yield: an accurate identification of the mobile device's present location, and further does not take into account the signal strength of both the new BTS and the last visited BTS as measured by the mobile device. In such a scenario, the mobile device may register prematurely, which can lead to an excessive number of registrations.
The art teachings, taken either singly or in combination, are not seen to describe the instant invention as claimed. Thus, a method for reducing the rate of registration in CDMA-based mobile networks solving the aforementioned problems is desired.